Would you ever post a photo on a profile which was not you??

When you create a profile on line, such as Yahoo, Yahoo Personals, Yahoo Answers, MySpace... have you ever used another person's photo you found to disguise your weight, height or looks?? Or have you swiped a picture of a model and claimed it to be you? If so, explain why you did, or you do... I don't understand why you would want to lie about who you are... I am curious.